The invention relates to medical balloons and especially to angioplasty dilatation balloon catheters.
Such balloons are intended to be collapsed to small size about their long supporting devices. In the case, e.g., of angioplasty balloon catheters, the small size is necessary to enable advance of the catheter through narrow and curved blood vessels into the region of stenosis where the balloon is to be inflated. After use, the balloon must be deflated and withdrawn. It is important in such movements not to damage the vessel walls or other delicate tissue of the body.
The process of making such balloons usually starts with an extruded cylindrical tube of a given diameter and wall thickness. The tube, in its amorphous state, is heated to blowing temperature and inflated and drawn longitudinally. Thus a tube of amorphous polyethylene terephthalate can be drawn and expanded to achieve a wall thickness of less than 0.001 inch in the main body of the balloon with wall thicknesses that increase in the tapered proximal and distal transition regions.
Whereas such balloons have been found to be quite useful, especially when high strength resins are employed to provide correspondingly high pressures of inflation, there have been disadvantages attributable to the thickness of the balloon material in the transition regions.
During folding of the balloon and wrapping it around the catheter shaft to make it small size for insertion, protruding bumps or distortions occur at the ends of the balloon. Because of the thickness of the material at these regions, these distortions can be relatively stiff and sharp and can cause trauma to the arteries or other passages through which the balloon is passed.
One area in which improvement is particularly needed in this regard is that of large diameter, high pressure angioplasty balloon catheters, i.e., balloon catheters in which the diameter of the main body of the balloon, when inflated, is between about 5 to 12 millimeters.
Also, known techniques have made it difficult to achieve balloon catheters for other applications, for instance, balloon catheters that require elonqated sleeves to fit tightly over very small catheters.